Hi The coolant level in my Skoda 2009 1.9 Octavia diesel est car has gone below minimum. I know best practice is said to be draining system and starting again with new fluid , but how important is it really and what sort of costs would that incur if done during a service ? Would it be asking for trouble just topping up with a compatible ? Obvs if I ask dealers they are going to say critical ! On other hand I intend to hang on to this car since I love it and only put on new tyres last year .

My first question would be, do you know why it's gone down? Are there signs of any leaks or smoke etc?

If nothing major, and I've had this on my own 1.9 TDI, I used a coolant sealant liquid (straight into the reservoir) and topped up and that worked a charm.

Definitely would not recommend adding any coolant sealant! - if the loss is only very minor and there are no obvious leaks, I'd suggest topping up with compatible coolant and closely monitoring the level.

If only adding a small quantity, safest to top up with concentrate rather than diluted coolant.

Do you know if the coolant has ever been replaced? It does have a limited service life for corrosion protection.

I drained mine for waterpump/timing replacement from bottom rad hose. Couldnt find a block drain plug so when removing waterpump found the excess that didnt drain. There was a fair bit left in engine so I dont think its possible to remove all coolant unless you can find a block drain plug. As long as its topped up with the same or if draining use the same as there will be residual in block unless you remove water pump. I would top up and monitor how much its using.

Mine was a 1.9tdi BXE

Alasdair

On 24/10/2025 at 21:09, Yop said:

but how important is it really

Provided you use compatible coolant to top up, not really necessary at all Id say.

How low is it?

Maybe need to bleed air out if gone really low.

But as said, find where it went and fix the leak

Thanks everyone for responses. No I dont know re whether coolant has ever been replaced as OH dealt with it all. Its done about 55k miles. I suddenly saw the symbol for low coolant flash, and a warning noise when I started car yesterday morning(so engine cold) Checked and found level about just under a cm below minimum . Only had 013ABJM1 VW's own version of G13 coolant in the garage bought in 2020 by my OH for his 2019 Superb, but didnt know whether it either could be out of date or even compatible in my cars G12 bottle , internet gave yeses and no's , Europarts said no, dealer said yes first, then to only top enough to get to garage and then theyd put the correct stuff in , so earlier just a bit bothered by topping up to see if level drops ,but will try it later . Couldnt see any leaks under car ,and no pink residue inside engine compartment or round bottle cap but presuming a significant leak as level so low and last years MOT supposedly checked level was correct . Its going in for a planned service anyway on Thurs ,so Ill get to know then I guess. Imagining water pump , radiator likely , hoping its not the metal pipes behind everything thats corroded that I read could be the issue .The cam belt and timing chain could apparently be due as well this year datewise anyway even if mileage low. Could be a mega expensive bill depending on what they find. Probably makes sense to get everything done at same time though - in the hope car stays good for many more years? Update as I failed to post this properly yesterday -- I sank a turkey baster into the bottle and drew some up from the bottom, it was crystal clear , so thats one piece of good news. Im grateful for all the imput from the forum, this and other threads Ive read , Ive learned a lot , so I might have a better chance of understanding what the garage is talking about now - Ill top up when it stops throwing it down ,drive it locally with a water bottle on the seat, and watch for a few days

9 hours ago, BlueWagon said:

Provided you use compatible coolant to top up, not really necessary at all Id say.

How low is it?

Maybe need to bleed air out if gone really low.

But as said, find where it went and fix the leak

Edited 26 October, 202526 Oct by Yop

4 minutes ago, Yop said:

Thanks everyone for responses. No I dont know re whether coolant has ever been replaced as OH dealt with it all. Its done about 50k miles. I suddenly saw the symbol for low coolant flash, and a warning noise when I started car yesterday morning(so engine cold) Checked and found level about just under a cm below minimum . Only had 013ABJM1 VW's own version of G13 coolant in the garage bought in 2020 by my OH for his 2019 Superb, but didnt know whether it either could be out of date or even compatible in my cars G12 bottle , internet gave yeses and no's , Europarts said no, dealer said yes first, then to only top enough to get to garage and then theyd put the correct stuff in , so earlier just a bit bothered by topping up to see if level drops ,but will try it later . Couldnt see any leaks under car ,and no pink residue inside engine compartment or round bottle cap but presuming a significant leak as level so low and last years MOT supposedly checked level was correct . Its going in for a planned service anyway on Thurs ,so Ill get to know then I guess. Imagining water pump , radiator likely , hoping its not the metal pipes behind everything thats corroded that I read could be the issue .The cam belt and timing chain could apparently be due as well this year datewise anyway even if mileage low. Could be a mega expensive bill depending on what they find. Probably makes sense to get everything done at same time though - in the hope car stays good for many more years? Update as I failed to post this properly yesterday -- I sank a turkey baster into the bottle and drew some up from the bottom, it was crystal clear , so thats one piece of good news. Im grateful for all the imput from the forum, this and other threads Ive read , Ive learned a lot , so I might have a better chance of understanding what the garage is talking about now - Ill top up when it stops throwing it down ,drive it locally with a water bottle on the seat, and watch for a few days

Use correct coolant, don't dilute by using plain water to top up.

Thanks, Ive got ionised but not distilled water here I was going to put in , I was worried about what Id read about despite the claim that G13 was backward compatible with G12, it still was far from ideal , thats why I presumed it would be better just to get the garage to put more of the correct concentrate in later ?

De-ionised water is fine to mix coolant to required strength - but I'd not recommend using it for top up unless in an emergency - and changed for correct coolant ASAP.

I agree with Warrior193 only use water as an emergency as it will eventually dilute coolant and you will lose frost protection and also anticorosion. Check the pasenger side carpet for dampness and crystal deposits. If there is no visible sign of coolant leak anywhere else it may be the heater matrix or pipes feeding it that are leaking. (hopefully not). Check your engine oil and cap for emulsification in case the head gasket has blown as well. A good tip is to park up on a dry surface like a garage or covered car park and check for drips. My old octavia used to leak slightly from a rad hose union but only when hot so coolant tended to evaporate. It did leave crystal deposits but was impossible to see as the undertray blocked the view.

Alasdair

Thanks again guys .Might try ringing the garage thats going to service it and see what they would have put in it ,and if they will sell me enough for the top up . Its not too unwalkable a distance. At least if I do the top up I can run the car round for a tryout and see if a leak appears, rather than do nothing and they come for it for the service and wont know without an expensive test ,whether it leaks or not.

Hi. Depends on age of car but my '54 Plate 2.0 TDi had a coolant bottle that had fatigued over time and the side had gone porous. I thought I was losing a bit of coolant due to a headgasket fault or a waterpump leak. Turns out it was the expansion bottle. Got one from Autodoc for around a Twenty and fitted it. Topped up with 1 liter of red coolant G12+ and it's been fine.